Solid-state lithium-ion conductor and methods of manufacture thereof

ABSTRACT

A solid-state ion conductor includes a compound of Formula (I):
 
Li 4+x B 7 O 12+0.5x X 1   a X 2   1−a    Formula (I)
 
wherein, in Formula (I), 0≤x≤1; X 1  is a pseudohalogen; X 2  is a halogen; and 0&lt;a≤1.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to U.S. Provisional Patent ApplicationNo. 63/150,693, filed on Feb. 18, 2021, in the United States Patent andTrademark Office, and all the benefits accruing therefrom under 35U.S.C. § 119, the content of which is incorporated herein in itsentirety by reference.

BACKGROUND (1) Field

Disclosed is a solid-state lithium-ion conductor and methods ofmanufacturing the solid-state lithium-ion conductor. Also disclosed is apositive electrode comprising the solid-state lithium-ion conductor, anegative electrode comprising the solid-state lithium-ion conductor, andan electrochemical cell comprising the solid-state lithium-ionconductor.

(2) Description of the Related Art

Solid-state lithium batteries can provide improved specific energy andenergy density and can avoid safety concerns associated with flammableorganic solvents used in liquid electrolytes. Oxide and sulfidesolid-state electrolytes have been used. Available sulfides can providegreater lithium conductivity than oxides, however they also presentsafety concerns, for example reaction with air or water to evolvehydrogen sulfide. Oxides can provide reduced toxicity relative tosulfides, and stability in air, but application of available oxides islimited because of their low conductivity or incompatibility withhigh-voltage cathode materials or lithium metal.

Thus, there remains a need for a solid-state electrolyte which providesimproved ionic conductivity and avoids the toxicity and safety concernsassociated with sulfides.

SUMMARY

Disclosed is a solid-state ion conductor comprising a compound ofFormula (I):Li_(4+x)B₇O_(12+0.5x)X¹ _(a)X² _(1−a)   Formula (I)wherein, in Formula (I), 0≤x≤1; X¹ is a pseudohalogen; X² is a halogen;and 0<a≤1.

Also disclosed is a positive electrode including: a positive activematerial layer including a lithium transition metal oxide, a lithiumtransition metal phosphate, or a combination thereof; and thesolid-state ion conductor on the positive active material layer.

Also disclosed is a negative electrode comprising: a negative activematerial layer comprising lithium metal, a lithium metal alloy, or acombination thereof; and the solid-state ion conductor on the negativeactive material layer.

Also disclosed is a negative electrode for a lithium secondary battery,the electrode comprising: a current collector; and the solid-state ionconductor on the current collector.

Also disclosed is an electrochemical cell including: a positiveelectrode; a negative electrode; and an electrolyte layer between thepositive electrode and the negative electrode, wherein at least one ofthe positive electrode, the negative electrode, or the electrolyte layerincludes the solid-state ion conductor.

BRIEF DESCRIPTION OF THE DRAWINGS

The following figures are exemplary embodiments wherein the likeelements are numbered alike, in which:

FIG. 1 shows an embodiment of a protected positive electrode;

FIG. 2 shows an embodiment of a protected negative electrode;

FIG. 3 shows an embodiment of a lithium battery;

FIG. 4 is a graph of the lithium diffusivity (cm²/s) versus temperature(K⁻¹) showing the results of Arrhenius analysis of Li₄B₇O₁₂OH;

FIG. 5 is a graph of the lithium diffusivity (cm²/s) versus temperature(K⁻¹) showing the results of Arrhenius analysis of Li₄B₇O₁₂SH;

FIG. 6 is a graph of the lithium diffusivity (cm²/s) versus temperature(K⁻¹) showing the results of Arrhenius analysis of Li₄B₇O₁₂NH₂;

FIG. 7 is a graph of the lithium diffusivity (cm²/s) versus temperature(K⁻¹) showing the results of Arrhenius analysis of Li₄B₇O₁₂Cl;

FIG. 8 is a graph of the lithium diffusivity (cm²/s) versus temperature(K⁻¹) showing the results of Arrhenius analysis of Li₄B₇O₁₂Br;

FIG. 9 is a graph of the lithium diffusivity (cm²/s) versus temperature(K⁻¹) showing the results of Arrhenius analysis of Li₁₀B₁₄O₂₅(OH)₂;

FIG. 10 is a graph of lithium-ion conductivity at 300K (millisiemens percentimeter, mS/cm) versus volume of the anion (cubic Angstroms, Å³) forvarious boracite-type materials.

FIG. 11 is a graph of intensity (arbitrary units, a.u.) versusdiffraction angle (degrees) showing a calculated X-ray powderdiffraction (XRD) pattern for Li₄B₇O₁₂OH, Li₄B₇O₁₂BH₄, and Li₄B₇O₁₂Cl;and

FIG. 12 shows an embodiment of the crystal structure of a solid-stateion conductor of the formula Li₄B₇O₁₂BH₄.

DETAILED DESCRIPTION

Currently available lithium-ion batteries have numerous safety issuesdue to the leakage and flammability of liquid organic electrolytes,which restrict their application in electric vehicles and grid-basedenergy storage infrastructure. In this case, solid-state batteries(SSBs) have been proposed as the next-generation batteries to addressthese limitations. Despite fast development in this arena, mostsolid-state lithium-ion conductors (SSLICs) are still far frompractical. Moreover, many state-of-the-art oxide SSLICs, such asLi₇La₃Zr₂O₁₂, contain rare-earth elements or noble metals, which canincrease the cost of the solid electrolyte. Therefore, it is desirableto discover new oxide SSLICs with high room-temperature ionicconductivity and lower cost elements.

The present inventors have discovered a solid-state ionic conductor thathas high ionic conductivity and is useful as a solid electrolyte in asolid-state battery. The disclosed solid-state ionic conductor has aboracite-type structure. In a further advantageous feature, borates canprovide a lower sintering temperature compared with other oxides, easingprocessing.

Accordingly, disclosed is a solid-state ion conductor comprising acompound of Formula (I):Li_(4+x)B₇O_(12+0.5x)X¹ _(a)X² _(1−a)   Formula (I)wherein, in Formula (I), 0≤x≤1; X¹ is a pseudohalogen; X² is a halogen;and 0<a≤1.

In Formula (I), X¹ may be a cluster anion such as BH₄ ⁻, BF₄ ⁻, AlH₄ ⁻,NH₂ ⁻, OH⁻, SH⁻, or a combination thereof. For example, X¹ may be NH₂ ⁻,OH⁻, SH⁻, or a combination thereof. X¹ being OH⁻, SH⁻, or a combinationthereof are mentioned. In an aspect, X¹ is OH⁻. In an aspect, X¹ is SH⁻.

X² of Formula (I) may be F⁻, Cl⁻, Br⁻, I⁻, or a combination thereof. Cl⁻and Br⁻ are specifically mentioned. In an aspect, X² is Cl⁻.

In an aspect, no excess lithium is present and x=0. In an aspect, theexcess lithium content can be 0<x≤1. A content of x=1 is also mentioned.In an aspect, 0.05≤x≤0.8, 0.1≤x≤0.6, or 0.2≤x≤0.4.

The content of the pseudohalogen a is 0<a≤1. In an aspect, a=1. In anaspect, 0.01≤a≤1, or 0.1≤a≤1, or 0.1≤a≤0.9, or 0.1≤a≤0.75, or 0.1≤a≤0.5,or 0.1≤a≤0.25.

In an aspect, the solid-state ion conductor may comprise, but is notlimited to, Li₄B₇O₁₂(OH), Li₄B₇O₁₂SH, Li₄B₇O₁₂NH₂, Li₄B₇O₁₂BH₄,Li₄B₇O₁₂BF₄, Li₄B₇O₁₂Al H₄, Li₁₀B₁₄O₂₅(OH)₂, Li₁₀B ₁₄O₂₅(SH)₂,Li₁₀B₁₄O₂₅(NH₂)₂, Li₁₀B₁₄O₂₅(BH₄)₂, Li₁₀B₁₄O₂₅(BF₄)₂, Li₁₀B₁₄O₂₅(AlH₄)₂,Li₁₀B₁₄O₂₅(OH)Cl, Li₁₀B₁₄O₂₅(SH)Br, Li₁₀B₁₄O₂₅(NH₂)Cl,Li₁₀B₁₄O₂₅(BH₄)Br, Li₁₀B₁₄O₂₅(BF₄)I, Li₁₀B₁₄O₂₅(AlH₄)Br,Li₄B₇O₁₂(OH)_(0.5)Cl_(0.5), Li₄B₇O₁₂(OH)_(0.5)Br_(0.5), orLi₄B₇O₁₂(OH)_(0.5)I_(0.5).

The solid-state ion conductor may have an ionic conductivity of equal toor greater than 1 ×10⁻⁴ millisiemens per centimeter (mS/cm), at 300Kelvin (K). For example, the solid-state ion conductor may have an ionicconductivity of 1×10⁻⁴ mS/cm to 1×10² mS/cm, 1×10⁻⁴ mS/cm to 20 mS/cm,1×10⁻⁴ mS/cm to 10 mS/cm, 1×10⁻⁴ mS/cm to 1 mS/cm, or 1×10⁻² mS/cm to 1mS/cm, at 300 K. Ionic conductivity may be determined by a compleximpedance method at 300 K, further details of which can be found in J.-M. Winand et al., “Measurement of Ionic Conductivity in SolidElectrolytes,” Europhysics Letters, vol. 8, no. 5, p. 447-452, 1989, thecontent of which is incorporated herein by reference in its entirety.

In a specific aspect, x=0, a=1, and X¹ is OH⁻, and the solid-state ionconductor is of the formula Li₄B₇O₁₂OH. When the solid-state ionconductor is Li₄B₇O₁₂OH, the ionic conductivity can be 1×10⁻⁴ mS/cm to1×10² mS/cm, or 1 mS/cm to 1×10² mS/cm.

In a specific aspect, x=1, a=1, and X¹ is OH⁻, and the solid-state ionconductor is of the formula Li₁₀B₁₄O₂₅(OH)₂. When the solid-state ionconductor is Li₁₀B₁₄O₂₅(OH)₂, the ionic conductivity can be 1×10⁻⁴ mS/cmto 10 mS/cm, or 1×10⁻⁴ mS/cm to 1 mS/cm.

In another specific aspect, x=0, a=1, and X¹ is SH⁻, and the solid-stateion conductor is of the formula Li₄B₇O₁₂SH. When the solid-state ionconductor is Li₄B₇O₁₂SH, the ionic conductivity can be 1×10⁻⁴ mS/cm to10 mS/cm, or 1×10⁻⁴ mS/cm to 1 mS/cm.

In another specific aspect, x=0, a=1, and X¹ is NH₂ ⁻, and thesolid-state ion conductor is of the formula Li₄B₇O₁₂NH₂. When thesolid-state ion conductor is Li₄B₇O₁₂NH₂, the ionic conductivity can be1×10⁻⁴ mS/cm to 1 mS/cm.

A method for the manufacture of the solid-state ion conductor is alsodisclosed. The solid-state ion conductor may be prepared using asolid-state synthesis method. For example, the solid-state ion conductormay be prepared by contacting precursor compounds, e.g., a lithiumcompound, a boron oxide, an X¹ precursor compound, and optionally, an X²precursor compound, in stoichiometric amounts to provide a mixturehaving a suitable stoichiometry of the elements of the productsolid-state ion conductor, and then treating the mixture to provide thesolid-state ion conductor of Formula (I). For example, the lithiumprecursor may be Li₂CO₃ or Li₂O, the boron precursor may be B₂O₃ orH₃BO₃, the X¹ precursor may be LiX¹, and the X² precursor (when present)may be LiX².

The treating may comprise any suitable method, e.g., heat-treating, ormechanochemically milling, e.g., ball milling, for example. Theheat-treating may use any suitable atmosphere, such as air, nitrogen,argon, helium, or a combination thereof, at a suitable temperature, suchas 400° C. to 1000° C., or 400° C. to 700° C., or 500° C. to 600° C.,for a time effective to provide the solid-state ion conductor, e.g., 0.5to 20 hours, 2 to 15 hours, or 3 to 10 hours, or 0.5 to 2 hours, or 0.7to 1 hour.

The mechanochemical milling can be conducted under any suitableatmosphere, e.g., in air, using any suitable medium, e.g., usingzirconia balls in a zirconia container. Use of milling for 1 to 100hours, or 10 to 30 hours, at 200 to 1000 revolutions per minute (RPM),225 to 600 RPM, or 250 to 450 RPM is mentioned. Additional details ofthe method can be determined by one of skill in the art without undueexperimentation.

The disclosed method provides the solid-state ion conductor havingdesirable ionic conductivity and stability, e.g., stability of 1.5 volts(V versus Li/Li⁺) to 5 V, e.g., 1.75 V to 4.8 V, 2 V to 4.6V, or 2.5 Vto 4.4 V, versus Li/Li⁺. In an aspect, the solid-state ion conductor isat least kinetically stable when contacted with a lithium transitionmetal oxide positive electrode active material, such as lithium nickelcobalt manganese oxide or lithium nickel cobalt aluminum oxide, alithium transition metal phosphate positive electrode active material,such as lithium iron phosphate, or is at least kinetically stable whencontacted with lithium metal, e.g., the solid-state ion conductor doesnot form an alloy or compound when contacted with lithium metal.

The solid-state ion conductor can be disposed on a positive activematerial layer to provide a protected positive electrode, shownschematically in FIG. 1 , which includes a current collector 101, apositive active material layer 102 and protection layer 103 comprisingthe solid-state ion conductor on the positive active material layer.While not wanting to be bound by theory, it is understood that use ofthe protection layer comprising the solid-state ion conductor can avoiddegradation of the positive active material, resulting in improvedperformance. The protection layer may be disposed on the positive activematerial layer by sputtering, for example, or by casting or coating thepositive active material layer with a coating composition comprising thesolid-state ion conductor and drying to remove a solvent of the coatingcomposition, for example.

The solid-state ion conductor can be disposed on a negative activematerial layer to provide a protected negative electrode, shownschematically in FIG. 2 , which includes a negative active materiallayer 201 disposed on a current collector 202, and a protection layer203 comprising the solid-state ion conductor on the negative activematerial layer. While not wanting to be bound by theory, it isunderstood that use of the protection layer comprising the solid-stateion conductor can avoid degradation of the negative active material,resulting in improved performance. The protection layer may be disposedon the negative active material layer by sputtering, for example, or bycasting or coating the negative active material layer with a coatingcomposition comprising the solid-state ion conductor and drying toremove a solvent of the coating composition, for example.

In an aspect, the solid-state ion conductor can alternatively bedisposed on a current collector to provide a negative electrode. Theprotection layer may be disposed on the negative active material layerby sputtering, for example, or by casting or coating the currentcollector with a coating composition comprising the solid-state ionconductor and drying to remove a solvent of the coating composition, forexample.

Also disclosed is an electrochemical cell (e.g., a lithium battery)comprising a positive electrode, a negative electrode, and anelectrolyte layer between the positive electrode and the negativeelectrode, wherein at least one of the positive electrode, the negativeelectrode or the electrolyte layer comprises the solid-state ionconductor of the present disclosure. For example, the solid-state ionconductor can be disposed between the positive electrode and thenegative electrode of a lithium battery and can serve as a solidelectrolyte in the lithium battery, shown schematically in FIG. 3 .Included in the lithium battery shown in FIG. 3 is a positive electrodecomprising a positive active material layer 301 on a positive currentcollector 302, an electrolyte layer 303, and a negative electrodecomprising a negative active material layer 304 on negative currentcollector 305. It is understood that the positive electrode couldalternatively be referred to as a cathode, and the negative electrode asan anode. The electrolyte layer may comprise the solid-state ionconductor. In an aspect, the electrolyte layer is suitably electricallyinsulating to serve as a separator to electrically isolate the positiveelectrode from the negative electrode. For the positive currentcollector aluminum or stainless steel may be used, and for the negativecurrent collector copper, stainless steel, or titanium may be used.

The electrolyte layer may alternatively or additionally comprise a solidelectrolyte other than or in addition to the solid-state ion conductor.The solid electrolyte may comprise, for example, an oxide solidelectrolyte or a sulfide solid electrolyte.

Examples of the oxide solid electrolyte may includeLi_(1+x+y)Al_(x)Ti_(2−x)Si_(y)P_(3−y)O₁₂ (where 0<x<2 and 0≤y<3),BaTiO₃, Pb(Zr_(a)Ti_(1−a))O₃ (PZT) where 0≤a≤1, Pb_(1−x)La_(x)Zr_(1−y)Ti_(y)O₃ (PLZT) where 0≤x<1 and 0≤y<1, Pb(Mg_(1/3)Nb_(2/3))O₃—PbTiO₃(PMN-PT), HfO₂, SrTiO₃, SnO₂, CeO₂, Na₂O, MgO, NiO, CaO, BaO, ZnO, ZrO₂,Y₂O₃, Al₂O₃, TiO₂, SiO₂, Li₃PO₄, Li_(x)Ti_(y)(PO₄)₃ (where 0<x<2 and0<y<3), Li_(x)Al_(y)Ti_(z)(PO₄)₃ where 0<x<2, 0<y<1, and 0<z<3,Li_(1+x+y)(Al_(a)Ga_(1−a))_(x)(Ti_(b)Ge_(1−b))_(2−x)Si_(y)P_(3−y)O₁₂where 0≤x≤1, 0≤y≤1, 0≤a≤1, and 0≤b≤1, Li_(x)La_(y)TiO₃ where 0<x<2 and0<y<3, Li₂O, LiOH, Li₂CO₃, LiAlO₂, Li₂O—Al₂O₃—SiO₂—P₂O₅—TiO₂—GeO₂, orLi_(3+x)La₃M₂O₁₂ where M is Te, Nb, or Zr, and 0≤x≤10. Also mentioned isa lithium garnet such as Li₇La₃Zr₂O₁₂ (LLZO) orLi_(3+x)La₃Zr_(2−a)Me_(a)O₁₂ (e.g., Me-doped LLZO, where Me is Ga, W,Nb, Ta, or Al, and 0≤x≤10 and 0≤a<2). A combination comprising at leastone of the foregoing may be used.

Examples of the sulfide solid electrolyte may include Li₂S—P₂S₅,Li₂S—P₂S₅—LiX (where X is a halogen element), Li₂S—P₂S₅—Li₂O,Li₂S—P₂S₅—Li₂O—LiI, Li₂S—SiS₂, Li₂S—SiS₂—LiI, Li₂S—SiS₂—LiBr,Li₂S—SiS₂—LiCl, Li₂S—SiS₂—B₂S₃—LiI, Li₂S—SiS₂—P₂S₅—LiI, Li₂S—B₂S₃,Li₂S—P₂S₅—Z_(m)S_(n) where m and n each are a positive number, Zrepresents any of Ge, Zn, and Ga, Li₂S—GeS₂, Li₂S—SiS₂—Li₃PO₄,Li₂S—SiS₂—Li_(p)MeO_(q) (where p and q each are a positive number, Merepresents at least one of P, Si, Ge, B, Al, Ga, or In),Li_(7−x)PS_(6−x)Cl_(x) (where 0≤x≤2), Li_(7−x)PS_(6−x)Br_(x) (where0≤x≤2), or Li_(7−x)PS_(6−x)I_(x) (where 0≤x≤2). The sulfide solidelectrolyte may include at least sulfur (S), phosphorus (P), and lithium(Li), as component elements among the sulfide solid electrolytematerials. For example, the sulfide solid electrolyte may be a materialincluding Li₂S—P₂S₅. Here, when the material including Li₂S—P₂S₅ is usedas a sulfide solid electrolyte material, a molar ratio of Li₂S and P₂S₅(Li₂S:P₂S₅) may be, for example, selected in a range of about 50:50 toabout 90:10. The sulfide solid electrolyte may also comprise anargyrodite-type solid electrolyte, such as Li_(7−x)PS_(6−x)Cl_(x) (where0≤x≤2), Li_(7−x)PS_(6−x)Br_(x) (where 0≤x≤2), or Li_(7−x)PS_(6−x)I_(x)(where 0≤x≤2), e.g., Li₆PS₅Cl, Li₆PS₅Br, or Li₆PS₅I.

The electrolyte layer comprising the solid-state ion conductor may benon-porous, or have a porosity of 0% (no pores) to 25%, based on a totalvolume of the electrolyte layer. The porosity may be, for example, 0% to25%, 1% to 20%, 5% to 15%, or 7% to 12%, based on a total volume of theelectrolyte layer. The porosity of electrolyte layer may be determinedby scanning electron microscopy, the details of which can be determinedby one of skill in the art without undue experimentation. Alternatively,porosity may be determined using nitrogen isotherms as disclosed in E.P. Barrett, L. G. Joyner, P. P. Halenda, “The determination of porevolume and area distributions in porous substances. I. Computations fromnitrogen isotherms,” J. Am. Chem. Soc. (1951), 73, 373-380, the detailsof which can be determined by one of skill in the art without undueexperimentation.

In an aspect, the electrolyte layer is porous, and an ionic liquid, apolymer-ionic liquid, a liquid electrolyte comprising a lithium salt andan organic solvent, or a combination thereof is disposed in a pore ofthe electrolyte layer to provide a hybrid electrolyte.

The ionic liquid (e.g., molten salt) may comprise i) an ammonium cation,a pyrrolidinium cation, a pyridinium cation, a pyrimidinium cation, animidazolium cation, a piperidinum cation, a pyrazolium cation, anoxazolium cation, a pyridazinium cation, a phosphonium cation, asulfonium cation, a triazolium cation, or a combination thereof, and ii)an anion, e.g., BF₄ ⁻, PF₆ ⁻, AsF₆ ⁻, SbF₆ ⁻, AlCl₄ ⁻, HSO₄ ⁻, ClO₄ ⁻,CH₃SO₃ ⁻, CF₃CO₂ ⁻, Cl⁻, Br⁻, I⁻, SO₄ ²⁻, CF₃SO₃ ⁻, (FSO₂)₂N⁻,(C₂F₅SO₂)₂N⁻, (C₂F₅SO₂)(CF₃SO₂)N⁻, (CF₃SO₂)₂N⁻, or a combinationthereof. Examples of the ionic liquid includeN-methyl-N-propylpyrrolidinium bis(trifluoromethylsulfonyl)imide,N-butyl-N-methyl-pyrrolidinium bis(trifluoromethylsulfonyl)imide,1-butyl-3-methyl-imidazolium bis(trifluoromethylsulfonyl)imide,1-ethyl-3-methyl-imidazolium bis(trifluoromethylsulfonyl)imide, or acombination thereof.

The polymer ionic liquid may be a polymerization product of ionic liquidmonomers, or a polymeric compound. The polymer ionic liquid may includea repeating unit that includes i) an ammonium cation, a pyrrolidiniumcation, a pyridinium cation, a pyrimidinium cation, an imidazoliumcation, a piperidinum cation, a pyrazolium cation, an oxazolium cation,a pyridazinium cation, a phosphonium cation, a sulfonium cation, atriazolium cation, or a combination thereof, and ii) an anion, e.g., BF₄⁻, PF₆ ⁻, AsF₆ ⁻, SbF₆ ⁻, AlCl₄ ⁻, HSO₄ ⁻, ClO₄ ⁻, CH₃SO₃ ⁻, CF₃CO₂ ⁻,(CF₃SO₂)₂N⁻, (FSO₂)₂N⁻, Cl⁻, Br⁻, I⁻, SO₄ ²⁻, CF₃SO₃ ⁻, (C₂F₅SO₂)₂N⁻,(C₂F₅SO₂)(CF₃SO₂)N⁻, NO₃ ⁻, Al₂Cl₇ ⁻, (CF₃SO₂)₃C⁻, (CF₃)₂PF₄ ⁻,(CF₃)₃PF₃ ⁻, (CF₃)₄PF₂ ⁻, (CF₃)₅PF⁻, (CF₃)₆P⁻, SF₅CF₂SO₃ ⁻, SF₅CHFCF₂SO₃⁻, CF₃CF₂(CF₃)₂CO⁻, (CF₃SO₂)₂CH⁻, (SF₅)₃C⁻, (O(CF₃)₂C₂(CF₃)₂O)₂PO—, or acombination thereof.

For the liquid electrolyte comprising a lithium salt and an organicsolvent, the lithium salt may be a lithium salt of BF₄ ⁻, PF₆ ⁻, AsF₆ ⁻,SbF₆ ⁻, AlCl₄ ⁻, HSO₄ ⁻, ClO₄ ⁻, CH₃SO₃ ⁻, CF₃CO₂ ⁻, (CF₃SO₂)₂N⁻,(FSO₂)₂N⁻, Cl⁻, Br⁻, I⁻, SO₄ ²⁻, CF₃SO₃ ⁻, (C₂F₅SO₂)₂N⁻,(C₂F₅SO₂)(CF₃SO₂)N⁻, NO₃ ⁻, Al₂Cl₇ ⁻, (CF₃SO₂)₃C⁻, (CF₃)₂PF₄ ⁻,(CF₃)₃PF₃ ⁻, (CF₃)₄PF₂ ⁻, (CF₃)₅PF⁻, (CF₃)₆P⁻, SF₅CF₂SO₃ ⁻, SF₅CHFCF₂SO₃⁻, CF₃CF₂(CF₃)₂CO⁻, (CF₃SO₂)₂CH⁻, (SF₅)₃C⁻, (O(CF₃)₂C₂(CF₃)₂O)₂PO, or acombination thereof. The organic solvent may comprise a carbonate suchas propylene carbonate, ethylene carbonate, fluoroethylene carbonate,butylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethylcarbonate, or a combination thereof.

The electrolyte layer may further comprise a separator film. Theseparator film may be electrically insulating, and may comprisepolyethylene, polypropylene, polyvinylidene fluoride, or a combinationthereof. For example, the separator film may be a multilayer separatorfilm, such as a two-layer separator of polyethylene/polypropylene, athree-layer separator of polyethylene/polypropylene/polyethylene, or athree-layer separator of polypropylene/polyethylene/polypropylene. Theseparator film may have a pore diameter of 0.01 μm to 10 μm, and athickness of 5 μm to 20 μm. If present, the liquid electrolyte, ionicliquid, or polymer ionic-liquid electrolyte may be disposed in a pore ofthe separator film.

In some embodiments, other electrolytes, including a liquid electrolyteor ionic-liquid (e.g., molten salt) electrolyte can be excluded from thedisclosed electrolyte layer.

The electrolyte layer may have any suitable thickness. A thickness ofthe solid electrolyte layer may be 1 to 300 μm, 2 to 100 μm, or 30 to 60μm.

The positive electrode comprises a positive active material layercomprising a lithium transition metal oxide, a lithium transition metalphosphate, or a combination thereof. For example, the positive activematerial can be a compound represented by any of Li_(a)M¹ _(1−b)M²_(b)D₂ wherein 0.90≤a≤1.8 and 0≤b≤0.5; Li_(a)E_(1−b)M² _(b)O_(2−c)D_(c)wherein 0.90≤a≤1.8, 0≤b≤0.5, and 0≤c≤0.05; LiE_(2−b)M² _(b)O_(4−c)D_(c)wherein 0≤b≤0.5 and 0≤c≤0.05; Li_(a)Ni_(1−b−c)Co_(b)M² _(c)D_(α) wherein0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05, and 0≤α≤2; Li_(a)Ni_(1−b−c)Co_(b)M²_(c)O_(2−α)X_(α) wherein 0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05, and 0<α<2;Li_(a)Ni_(1−b−c)Co_(b)M² _(c)O_(2−α)X₂ wherein 0.90≤a≤1.8, 0≤b≤0.5,0≤c≤0.05, and 0<α<2; Li_(a)Ni_(1−b−c)Mn_(b)M² _(c)D_(α) wherein0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05, and 0<α<2; Li_(a)Ni_(1−b−c)Mn_(b)M²_(c)O_(2−a)X_(α) wherein 0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05, and 0<α<2;Li_(a)Ni_(1−b−c)Mn_(b)M² _(c)O_(2−α)X₂ wherein 0.90≤a≤1.8, 0≤b≤0.5,0≤c≤0.05, and 0<α<2; Li_(a)Ni_(b)E_(c)G_(d)O₂ wherein 0.90≤a≤1.8,0≤b≤0.9, 0≤c≤0.5, and 0.001≤d≤0.1; Li_(a)Ni_(b)Co_(c)Mn_(d)GeO₂ wherein0.90≤a≤1.8, 0≤b≤0.9, 0≤c≤0.5, 0≤d≤0.5, and 0.001≤e≤0.1; Li_(a)NiG_(b)O₂wherein 0.90≤a≤1.8 and 0.001≤b≤0.1; Li_(a)CoG_(b)O₂ wherein 0.90≤a≤1.8and 0.001≤b≤0.1; Li_(a)MnG_(b)O₂ where 0.90≤a≤1.8 and 0.001≤b≤0.1;Li_(a)Mn₂G_(b)O₄ wherein 0.90≤a≤1.8 and 0.001≤b≤0.1; QO₂; QS₂; LiQS₂;V₂O₅; LiV₂O₂; LiRO₂; LiNiVO₄; Li_((3−f))J₂(PO₄)₃ (0≤f≤2);Li_((3−f))Fe₂(PO₄)₃ wherein 0≤f≤2; or LiFePO₄, in which in the foregoingpositive active materials M¹ is Ni, Co, or Mn; M² is Al, Ni, Co, Mn, Cr,Fe, Mg, Sr, V, or a rare-earth element; D is O, F, S, or P; E is Co orMn; X is F, S, or P; G is Al, Cr, Mn, Fe, Mg, La, Ce, Sr, or V; Q is Ti,Mo or Mn; R is Cr, V, Fe, Sc, or Y; and J is V, Cr, Mn, Co, Ni, or Cu.Examples of the positive active material include LiCoO₂, LiMn_(x)O_(2x)where x=1 or 2, LiNi_(1−x)Mn_(x)O_(2x) where 0<x<1,LiNi_(1−x−y)Co_(x)Mn_(y)O₂ where 0≤x≤0.5 and 0≤y≤0.5,LiNi_(1−x−y)Co_(x)Al_(y)O₂ where 0≤x≤0.5 and 0≤y≤0.5, LiFePO₄, TiS₂,FeS₂, TiS₃, or FeS₃. For example, the positive active material maycomprise NMC 811 (LiNi_(0.8)Mn_(0.1)Co_(0.1)O₂), NMC 622(LiNi_(0.6)Mn_(0.2)Co_(0.2)O₂), NMC 532 (LiNi_(0.5)Mn_(0.3)Co_(0.2)O₂),or NCA (LiNi_(0.8)Co_(0.15)Al_(0.05)O₂).

The positive active material layer may further include a binder. Abinder can facilitate adherence between components of the positiveactive material layer, and adherence of the positive active materiallayer to the current collector. Examples of the binder can includepolyacrylic acid (PAA), polyvinylidene fluoride, polyvinyl alcohol,carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose,regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene,polyethylene, polypropylene, ethylene-propylene-diene monomer (EPDM),sulfonated EPDM, styrene-butadiene-rubber, fluorinated rubber, acopolymer thereof, or a combination thereof. The amount of the bindercan be in a range of about 1 part by weight to about 10 parts by weight,for example, in a range of about 2 parts by weight to about 7 parts byweight, based on a total weight of the positive active material. Whenthe amount of the binder is in the range above, e.g., about 1 part byweight to about 10 parts by weight, the adherence of the electrode tothe current collector may be suitably strong.

The positive active material layer may further include a conductiveagent. Any suitable conductive agent may be used. The conductive agentmay comprise a carbon, a metal, or an oxide. The carbon may comprisecarbon black, carbon fiber, graphite, carbon nanotubes, graphene, or acombination thereof. The carbon black can be, for example, acetyleneblack, Ketjen black, Super P carbon, channel black, furnace black, lampblack, thermal black, or a combination thereof. The graphite can be anatural graphite or an artificial graphite. The metal may comprise ametal element, e.g., nickel, and may by in the form of a fiber orpowder, such as aluminum powder or a nickel powder. The conductive agentmay comprise an oxide, such as a zinc oxide or a potassium titanate; ora conductive polymer, such as a polyethylene oxide or a polyphenylenederivative. A combination comprising at least one of the foregoingconductive agents may be used. An amount of the conducting agent may befrom about 1 part by weight to about 10 parts by weight, for example,from about 2 parts by weight to about 5 parts by weight, based on 100parts by weight of the total weight of the positive active material.

The positive active material layer may further comprise the solid-ionconductor, or alternatively or additionally comprise a solid electrolyteother than or in addition to the solid-state ion conductor. The solidelectrolyte may comprise, for example, the oxide solid electrolyte, thesulfide solid electrolyte, or a combination thereof.

The positive active material layer may be disposed on the surface of asubstrate, e.g., an aluminum foil current collector, using any suitablemeans, for example, using tape casting, slurry casting (i.e., slurrycoating), or screen printing. Additional details of tape casting, slurrycoating, and screen printing, for example suitable binders and solvents,can be determined by one of skill in the art without undueexperimentation. For example, N-methylpyrollidone may be used as thesolvent.

The positive active material layer may have any suitable thickness,e.g., a thickness of 1 to 300 μm, 2 μm to 100 μm, or 30 to 60 μm.

The negative electrode may comprise a negative active material layer ona current collector. The negative active material layer may comprisecarbon, a non-transition metal oxide, lithium metal, a lithium metalalloy, or a combination thereof. The carbon may comprise naturalgraphite or artificial graphite, each of which may be crystalline oramorphous. Examples of the amorphous carbon include soft carbon, hardcarbon, mesocarbon, mesophase pitch carbon, and calcined coke. Thenon-transition metal oxide may comprise SnO_(x) where 0<x≤2, or SiO_(x)where 0<x≤2. The lithium metal alloy for the negative electrode mayinclude lithium, and a metal or metalloid alloyable with lithium.Examples of the metal or metalloid alloyable with lithium include Si,Sn, Al, Ge, Pb, Bi, Sb, a Si—Y′ alloy (wherein Y′ is at least one of analkali metal, an alkaline earth metal, a Group 13 to Group 16 element, atransition metal, or a rare earth element, except for Si), or a Sn—Y′alloy (wherein Y′ is at least one of an alkali metal, an alkaline earthmetal, a Group 13 to Group 16 element, a transition metal, or a rareearth element, except for Sn). Y′ may be Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti,Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os,Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Ge, P, As,Sb, Bi, S, Se, Te, Po, or a combination thereof. The current collectorfor the negative electrode may be copper or titanium, for example.

The negative electrode active material layer may comprise a binder as isfurther disclosed above. The negative active material layer may bedisposed on the surface of a substrate, e.g., a copper or titanium foilcurrent collector using any suitable means, for example, using tapecasting, slurry casting, or screen printing. Additional details of tapecasting and screen printing, for example suitable binders and solvents,can be determined by one of skill in the art without undueexperimentation. For example, N-methylpyrollidone may be used as thesolvent.

The negative active material layer may further comprise the solid-stateion conductor, or alternatively or additionally comprise a solidelectrolyte other than or in addition to the solid-state ion conductor.The solid electrolyte may comprise, for example, the oxide solidelectrolyte, the sulfide solid electrolyte, or a combination thereof.

The negative electrode may be an “anode-free” or “anodeless” typewherein lithium is not initially present in the negative electrode. Inthe “anode-free” type negative electrode, the negative electrode mayinitially comprise a current collector and a solid electrolyte, e.g.,the solid-state ion conductor of Formula (I), or alternatively or inaddition at least one of the oxide solid electrolyte or the sulfidesolid electrolyte on the current collector. In an aspect, thesolid-state ion conductor, the solid electrolyte, or a combinationthereof is directly on the current collector. Charging the battery candeposit lithium to form the negative active material layer on thecurrent collector, e.g., to deposit lithium metal or form a lithiummetal alloy on the current collector. The solid-state ion conductor ofFormula (I), or alternatively or in addition at least one of the oxidesolid electrolyte or the sulfide solid electrolyte may be disposed onthe current collector by sputtering or coating, for example.

The lithium battery can be manufactured by providing the positiveelectrode, providing the negative electrode, and disposing thesolid-state ion conductor comprising the compound according to Formula(I) between the position electrode and the negative electrode. Forexample, a lithium battery can be manufactured by sputtering thesolid-state ion conductor comprising the compound according to Formula(I) on the positive active material layer, disposing a negativeelectrode thereon, winding or folding the resulting structure, and thenenclosing the wound or folded structure in a cylindrical or rectangularbattery case or pouch to provide the lithium battery.

This disclosure is further illustrated by the following examples, whichare non-limiting.

EXAMPLES Ionic Conductivity Analysis

The ionic conductivities of various compounds according to Formula (I)were determined by ab-initio molecular dynamics (AIMD) calculationsusing the Vienna Ab Initio Simulation Package. Relevant parameters ofthe calculation include projector augmented wave potentials with akinetic energy cutoff of 400 eV, the exchange and correlationfunctionals of Perdew-Burke-Ernzerhof generalized gradient (GGA-PBE),and 200 picoseconds simulation time with a time step of 2 femtoseconds.For comparison, the ionic conductivity was also determined forLi₄B₇O₁₂Cl, Li₄B₇O₁₂Br, and Li₁₀B₁₄O₂₅(OH)₂.

Shown in FIG. 4 is an Arrhenius plot of the simulation results forLi₄B₇O₁₂OH. The activation energy was 0.228 electron volts (eV) and theionic conductivity at 300 K was 13.75 mS/cm.

Shown in FIG. 5 is an Arrhenius plot of the simulation results forLi₄B₇O₁₂SH. The activation energy was 0.321 electron volts (eV) and theionic conductivity at 300 K was 0.300 mS/cm.

Shown in FIG. 6 is an Arrhenius plot of the simulation results forLi₄B₇O₁₂NH₂. The activation energy was 0.496 electron volts (eV) and theionic conductivity at 300 K was 5.09×10⁻³ mS/cm.

Shown in FIG. 7 is an Arrhenius plot of the simulation results forLi₄B₇O₁₂Cl as a comparative example. The activation energy was 0.284electron volts (eV) and the ionic conductivity at 300 K was 0.508 mS/cm.

Shown in FIG. 8 is an Arrhenius plot of the simulation results forLi₄B₇O₁₂Br as a comparative example. The activation energy was 0.380electron volts (eV) and the ionic conductivity at 300 K was 0.033 mS/cm.

Shown in FIG. 9 is an Arrhenius plot of the simulation results forLi₁₀B₁₄O₂₅(OH)₂. The activation energy was 0.341 electron volts (eV) andthe ionic conductivity at 300 K was 0.185 mS/cm.

The relationship between ionic conductivity and the size of the anion(e.g., X¹) is shown in FIG. 10 and Table 1. From FIG. 10 and Table 1, itcan be seen that the ionic conductivity decreases with increasing anion(X¹) size.

TABLE 1 Composition Conductivity (mS/cm) Li₄B₇O₁₂Cl 0.508 Li₄B₇O₁₂Br0.033 Li₄B₇O₁₂I <10⁻⁸   Li₄B₇O₁₂OH 13.75  Li₄B₇O₁₂NH₂ 5.09 × 10⁻³Li₄B₇O₁₂SH 0.300 Li₄B₇O₁₂BH₄ <10⁻⁸   Li₄B₇O₁₂BF₄ <10⁻⁸   Li₄B₇O₁₂AlH₄<10⁻⁸   Li₁₀B₁₄O₂₅Cl₂ Low Li₁₀B₁₄O₂₅(OH)₂ 0.185

These results illustrate that the compound of Formula (I) providesunexpectedly improved conductivity. In a particularly surprising result,it can be seen that a high room temperature ionic conductivity of over10 mS/cm can be achieved by at least partially substituting a halide ionwith a hydroxide ion.

The various compounds described above may be prepared according to thefollowing methods.

Example 1. Li₄B₇O₁₂OH

Stoichiometric amounts of Li₂CO₃, B₂O₃ and LiOH will be combined toprovide a mixture. The mixture will be mechanically milled at 600 RPMfor 12 hours and heat treated at 800° C. for 24 hours in argonatmosphere to provide Li₄B₇O₁₂OH. The product will be analyzed by X-raypowder diffraction (XRD) using CuKα radiation, and XRD analysis willshow that Li₄B₇O₁₂OH is prepared.

A simulated XRD spectrum for Li₄B₇O₁₂OH is shown in FIG. 11 . Also shownin FIG. 11 for reference is a simulated XRD spectrum of Li₄B₇O₁₂Cl.

Example 2. Li₄B₇O₁₂SH

Stoichiometric amounts of Li₂CO₃, B₂O₃ and LiSH will be combined toprovide a mixture. The mixture will be mechanically milled at 600 RPMfor 24 hours and heat treated at 400° C. for 48 hours in H₂S atmosphereto provide Li₄B₇O₁₂SH. The product will be analyzed by X-ray powderdiffraction (XRD) using CuKα radiation, XRD analysis will show thatLi₄B₇O₁₂SH is prepared.

Example 3. Li₄B₇O₁₂NH₂

Stoichiometric amounts of Li₂CO₃, B₂O₃ and LiNH₂ will be combined toprovide a mixture. The mixture will be mechanically milled at 600 RPMfor 24 hours and heat treated at 400° C. for 48 hours in NH₃ atmosphereto provide Li₄B₇O₁₂NH₂. The product will be analyzed by X-ray powderdiffraction (XRD) using CuKα radiation, and XRD analysis will show thatLi₄B₇O₁₂NH₂ is prepared.

Example 4. Li₄B₇O₁₂BH₄

Stoichiometric amounts of Li₂CO₃, B₂O₃ and LiBH₄ will be combined toprovide a mixture. The mixture will be mechanically milled at 600 RPMfor 48 hours and heat treated at 300° C. for 48 hours in a hydrogenatmosphere to provide Li₄B₇O₁₂BH₄. The product will be analyzed by X-raypowder diffraction (XRD) using CuKα radiation, and XRD analysis willshow that Li₄B₇O₁₂BH₄ is prepared.

A simulated XRD spectrum for Li₄B₇O₁₂BH₄ is shown in FIG. 11 . Alsoshown in FIG. 11 for reference is a simulated XRD spectrum ofLi₄B₇O₁₂Cl.

A simulated crystal structure for Li₄B₇O₁₂BH₄ is shown in FIG. 12 .

Example 5. Li₄B₇O₁₂AlH₄

Stoichiometric amounts of Li₂CO₃, B₂O₃ and LiAlH₄ will be combined toprovide a mixture. The mixture will be mechanically milled at 600 RPMfor 48 hours and heat treated at 120° C. for 96 hours in hydrogenatmosphere to provide Li₄B₇O₁₂AlH₄. The product will be analyzed byX-ray powder diffraction (XRD) using CuKα radiation, and XRD analysiswill show that Li₄B₇O₁₂AlH₄ is prepared.

Example 6. Li₄B₇O₁₂BF₄

Stoichiometric amounts of Li₂CO₃, B₂O₃ and LiBF₄ will be combined toprovide a mixture. The mixture will be mechanically milled at 600 RPMfor 24 hours and heat treated at 500° C. for 48 hours in argonatmosphere to provide Li₄B₇O₁₂BF₄. The product will be analyzed by X-raypowder diffraction (XRD) using CuKα radiation, and XRD analysis willshow that Li₄B₇O₁₂BF₄ is prepared.

Example 7. Li_(4+x)B₇O_(12+0.5x)X¹ _(a)X² _(1−a), where X¹ is OH, X² isCl, Br, or I, and a<1 Compounds of Formula 1 where a<1, i.e., comprisinga combination of X¹ and X² will be prepared using the methods disclosedherein. The compositions in Table 2 will provide unexpectedconductivity.

TABLE 2 Composition Li₄B₇O₁₂(OH)_(0.5)Cl_(0.5)Li₄B₇O₁₂(OH)_(0.5)Br_(0.5) Li₄B₇O₁₂(OH)_(0.5)I_(0.5)

Various embodiments are shown in the accompanying drawings. Thisinvention may, however, be embodied in many different forms, and shouldnot be construed as limited to the embodiments set forth herein. Rather,these embodiments are provided so that this disclosure will be thoroughand complete, and will fully convey the scope of the invention to thoseskilled in the art. Like reference numerals refer to like elementsthroughout.

It will be understood that when an element is referred to as being “on”another element, it can be directly on the other element or interveningelements may be present therebetween. In contrast, when an element isreferred to as being “directly on” another element, there are nointervening elements present.

It will be understood that, although the terms “first,” “second,”“third,” etc. may be used herein to describe various elements,components, regions, layers, or sections, these elements, components,regions, layers, or sections should not be limited by these terms. Theseterms are only used to distinguish one element, component, region,layer, or section from another element, component, region, layer orsection. Thus, “a first element,” “component,” “region,” “layer,” or“section” discussed below could be termed a second element, component,region, layer or section without departing from the teachings herein.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting. As used herein, thesingular forms “a,” “an,” and “the” are intended to include the pluralforms, including “at least one,” unless the content clearly indicatesotherwise. “At least one” is not to be construed as limiting “a” or“an.” “Or” means “and/or.” It will be further understood that the terms“comprises” and/or “comprising,” or “includes” or “including” when usedin this specification, specify the presence of stated features, regions,integers, steps, operations, elements, or components, but do notpreclude the presence or addition of one or more other features,regions, integers, steps, operations, elements, components, or groupsthereof.

Spatially relative terms, such as “beneath,” “below,” “lower,” “above,”“upper” and the like, may be used herein for ease of description todescribe one element or feature's relationship to another element(s) orfeature(s) as illustrated in the figures. It will be understood that thespatially relative terms are intended to encompass differentorientations of the device in use or operation in addition to theorientation depicted in the figures. For example, if the device in thefigures is turned over, elements described as “below” or “beneath” otherelements or features would then be oriented “above” the other elementsor features. Thus, the exemplary term “below” can encompass both anorientation of above and below. The device may be otherwise oriented(rotated 90 degrees or at other orientations) and the spatially relativedescriptors used herein interpreted accordingly.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which this disclosure belongs. It willbe further understood that terms, such as those defined in commonly useddictionaries, should be interpreted as having a meaning that isconsistent with their meaning in the context of the relevant art and thepresent disclosure, and will not be interpreted in an idealized oroverly formal sense unless expressly so defined herein.

Exemplary embodiments are described herein with reference to crosssection illustrations that are schematic illustrations of idealizedembodiments. As such, variations from the shapes of the illustrations asa result, for example, of manufacturing techniques and/or tolerances,are to be expected. Thus, embodiments described herein should not beconstrued as limited to the particular shapes of regions as illustratedherein but are to include deviations in shapes that result, for example,from manufacturing. For example, a region illustrated or described asflat may, typically, have rough and/or nonlinear features. Moreover,sharp angles that are illustrated may be rounded. Thus, the regionsillustrated in the figures are schematic in nature and their shapes arenot intended to illustrate the precise shape of a region and are notintended to limit the scope of the present claims.

“Oxidation state” as used herein is a formalism used to describe ahypothetical charge that an atom would have if all bonds to atoms ofdifferent elements were 100% ionic, with no covalent component.

“Group” means a group of the Periodic Table of the Elements according tothe International Union of Pure and Applied Chemistry (“IUPAC”) Group1-18 group classification system.

While a particular embodiment has been described, alternatives,modifications, variations, improvements, and substantial equivalentsthat are or may be presently unforeseen may arise to applicants orothers skilled in the art. Accordingly, the appended claims as filed andas they may be amended are intended to embrace all such alternatives,modifications variations, improvements, and substantial equivalents.

What is claimed is:
 1. A solid-state ion conductor comprising a compoundof Formula (I):Li_(4+x)B₇O_(12+0.5x)X¹ _(a)X² _(1−a)   Formula (I) wherein, in Formula(I), 0≤x≤1; X¹ is BH₄ ⁻, BF₄ ⁻, AlH₄ ⁻, NH₂ ⁻, OH⁻, SH⁻, or acombination thereof; X² is a halogen; and 0<a≤1.
 2. The solid-state ionconductor of claim 1, wherein X² is F⁻, Cl⁻, Br⁻, I⁻, or a combinationthereof.
 3. The solid-state ion conductor of claim 1 having an ionicconductivity of greater than 10⁻⁴ mS/cm at 300 K.
 4. The solid-state ionconductor of claim 1, wherein x=0.
 5. The solid-state ion conductor ofclaim 1, wherein 0<x≤1.
 6. The solid-state ion conductor of claim 1,wherein a=1.
 7. The solid-state ion conductor of claim 1, wherein X¹ isNH₂ ⁻, OH⁻, SH⁻, or a combination thereof.
 8. The solid-state ionconductor of claim 1, wherein X¹ is OH⁻, SH⁻, or a combination thereof.9. The solid-state ion conductor of claim 1, wherein X¹ is OH⁻.
 10. Thesolid-state ion conductor of claim 9 having an ionic conductivity ofgreater than 1 mS/cm at 300 K.
 11. The solid-state ion conductor ofclaim 1, wherein X¹ is SH⁻.
 12. The solid-state ion conductor of claim11, having an ionic conductivity of greater than 1 mS/cm at 300 K.
 13. Amethod of preparing a solid-state ion conductor, the method comprising:contacting a lithium compound; a boron oxide; an X¹ precursor; andoptionally, an X² precursor; to provide a mixture; and treating themixture to provide the compound of Formula (I)Li_(4+x)B₇O_(12+0.5x)X¹ _(a)X² _(1−a)   Formula (I), wherein, in Formula(I), 0≤x≤1; X¹ is BH₄ ⁻, BF₄ ⁻, AlH₄ ⁻, NH₂ ⁻, OH⁻, SH⁻, or acombination thereof; X² is a halogen; and 0<a≤1.
 14. A positiveelectrode comprising: a positive active material layer comprising alithium transition metal oxide, a lithium transition metal phosphate, ora combination thereof; and the solid-state ion conductor of claim 1 onthe positive active material layer.
 15. A negative electrode comprising:a negative active material layer comprising lithium metal, a lithiummetal alloy, or a combination thereof; and the solid-state ion conductorof claim 1 on the negative active material layer.
 16. A negativeelectrode for a lithium secondary battery, the electrode comprising: acurrent collector; and the solid-state ion conductor of claim 1 on thecurrent collector.
 17. An electrochemical cell comprising: a positiveelectrode; a negative electrode; and an electrolyte layer between thepositive electrode and the negative electrode; wherein at least one ofthe positive electrode, the negative electrode, or the electrolyte layercomprises the solid-state ion conductor of claim
 1. 18. The solid-stateion conductor of claim 1, comprising Li₄B₇O₁₂(OH), Li₄B₇O₁₂SH,Li₄B₇O₁₂NH₂, Li₄B₇O₁₂BH₄, Li₄B₇O₁₂BF₄, Li₄B₇O₁₂AlH₄, Li₁₀B₁₄O₂₅(OH)₂,Li₁₀B₁₄O₂₅(SH)₂, Li₁₀B₁₄O₂₅(NH₂)₂, Li₁₀B₁₄O₂₅(BH₄)₂, Li₁₀B₁₄O₂₅(BF₄)₂,Li₁₀B₁₄O₂₅(AlH₄)₂, Li₁₀B₁₄O₂₅(OH)Cl, Li₁₀B₁₄O₂₅(SH)Br,Li₁₀B₁₄O₂₅(NH₂)Cl, Li₁₀B₁₄O₂₅(BH₄)Br, Li₁₀B₁₄O₂₅(BF₄)I,Li₁₀B₁₄O₂₅(AlH₄)Br, Li₄B₇O₁₂(OH)_(0.5)Cl_(0.5),Li₄B₇O₁₂(OH)_(0.5)Br_(0.5), or Li₄B₇O₁₂(OH)_(0.5)I_(0.5).
 19. Thesolid-state ion conductor of claim 1, comprising Li₄B₇O₁₂(OH),Li₄B₇O₁₂SH, Li₄B₇O₁₂NH₂, Li₄B₇O₁₂BH₄, Li₄B₇O₁₂BF₄, Li₄B₇O₁₂AlH₄,Li₁₀B₁₄O₂₅(OH)₂, Li₄B₇O₁₂(OH)_(0.5)Cl_(0.5), Li₄B₇O₁₂(OH)_(0.5)Br_(0.5),or Li₄B₇O₁₂(OH)_(0.5)I_(0.5).